gear sizes of ITR IBM models

Discussion in 'Electric Horology' started by paradise, Jul 16, 2013.

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  1. paradise

    paradise Registered User
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    Jun 24, 2007
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    I recently got several IBM master clock works all of seconds beat. In measuring the diameter of each gear of each model I noticed a variation of 30 or up to 60K difference yet what installed they all seemed to be interchangeable. I know clock gears do allow some slack which frequently saves me when I make a gear but I am never that far off. My question is is anyone familiar with this difference in the gear sizes. To be a little kmore specific I have one works with a coil spring and one with a ribbon spring and I can interchange any and all of their gears yet when I measure them each corresponding gear shows as much as A tenth of an inch difference in matched pairs. As a matter of curiousity I am wondering if anyone has any information on this and if anyone has experienced the same thing. I appreciate any information the list can contribute. I am a big IBM fan and have over a dozen of their master clocks and very much enjoy working with them. Thank you paradiseclocks
     
  2. eskmill

    eskmill Registered User
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    A very interesting observation but begs more data. Where were these IBM Master clock movements produced?

    Movements made in or for use in England, Germany and other IBM World Trade Corporations might have very slightly different tolerances but the general design remained rather constant over many years.

    We are led to believe that all US domestic IBM clock movements were made in or around Endicott New York but some movements could have been produced by other US manufacturers.

    I personally have at least one IBM Master movement that has the helical mainspring that can only provide less than an hour's running. It is a very old movement and needs only six volts for the winding magnets.

    Another movement I have, a 72 beat version, has solid steel plates with gold electroplate. It was made during WWII to comply with US War Department requirements to conserve brass. All its parts will interchange with older 72 beat movements that are all brass.

    It would be very interesting and informative if you would dissect several of your dozen IBM master movements, measure and catalog each example with photographs.

    The IBM master movement undoubtedly did undergo constant engineering changes but the general design had to remain relatively constant in order to supply maintenance parts and to assure compatibility.

    Thank you for your post. I am certain that others will comment.
     
  3. harold bain

    harold bain Registered User
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    It makes me wonder if the gears may have been outsourced, or if the specs changed over the years. It likely didn't have an effect on the quality of the movement. I've never seen one showing any wear on the gears or pinions.
    Good to hear someone has more of these than I do (I stopped at 5):whistle:
     
  4. paradise

    paradise Registered User
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    I will try to get more precise information along with some pics but it will not be quick. Aside from that I am slow, I also have to find the room to have a few of those guys apart at the same time and then learn how to post pictures; but I'll try.
     
  5. paradise

    paradise Registered User
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    Well I did some measuring and discovered that 20 or 30 thou. is about the max difference between wheels and the pinions can also vary as much as 10 thou. There doesn't seem to be any consistency as to which wheels and pinions measure out as same. In spite of the differences in sizes the fit seems to be fine. when assembled with any of the wheels, changing out several, they all spin fine. I even used 4 different sets of plates, still spun just fine. I don't think wear is the culprit here, IBM gears really didn't wear out very much, maybe never. So what comes to mind is that as each gear was made there was an allowable deviation from the standard which would still be acceptable. Here comes the pictures [ attempt ] P1010094.jpg P1010095.jpg P1010096.jpg P1010097.jpg
     
  6. eskmill

    eskmill Registered User
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    Thank you for the photos of clock movement wheels taken from IBM or International master clock movements.

    It is interesting that the outside diameter or tooth tip to tooth tip measurement varies and could be important but what really matters is he diameter of the tooth pitch circle. The pitch circles of the wheel and mating pinion must intersect, else there is excessive friction causing wear of both the wheel and pinion teeth.

    In design or repair when replacing a wheel or pinion, a depthing tool is commonly used to examine the tooth engagement. I don't have one but sometimes insert the wheel and pinion sets alone between the plates. If the wheel to pinion engagement is noisy when the wheel drives the pinion, then there will be friction and consequential wear.
     
  7. praezis

    praezis Registered User

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    Being no IBM expert at all, I discovered on the Photos, that the wheels w/ spokes seem to have involute teeth, while the solid wheel has cycloid teeth. That would explain the different tooth tip diameters.
    Frank
     

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